This invention relates generally to air ducts for residential and commercial use made from resin bonded fiber glass. More specifically, the invention relates to an improved air duct manufactured from resin-bonded fiber glass that includes an improved interior flowing air surface having a rated capacity air flow of up to about 5,000 feet per minute with less turbulence than is presently experienced in ducts whose rated capacity is approximately one-half that value. The invention further includes improved means for sanitizing the duct.
Currently, air ducts are manufactured from resin-bonded fiber glass formed into rigid, rectangular boards. Air duct systems manufactured from such boards are used in commercial and residential air-handling installations for cooling, heating, or dual-temperature service. The operating temperatures range up to 250.degree. F. with a maximum air velocity of 2,400 feet per minute and 2-inch water gauge static pressure. Air-handling systems made from such materials provide the combined benefits of good thermal insulation, vapor retardation, noise absorption, low leakage and easy fabrication.
Despite the above-described advantages, current construction requirements demand even higher performance. Specifically, exposed fiber glass board will often accumulate dirt, dust, and microorganisms if not adequately cleaned and it is difficult as well as expensive to clean the inside of an insulated duct. Further, fiber glass board is relatively rough and such roughness results in turbulent flow at the board surface thereby causing increased friction loss and requiring additional energy to pump air through the ducts.
One previous attempt at solving the aforenoted problems has been the application of an acrylic coating on the surfaces of the fiber glass board exposed to the flowing air. However, a significant amount of turbulence still exists during normal operating conditions even with the use of acrylic coatings. Thus an even greater degree of laminar flow adjacent to the interior surface of the duct board is desired. Further, the acrylic does not provide as smooth an interior surface as desired and therefore dirt, dust and microorganisms still accumulate in the interior surfaces of acrylic treated ducts. Unsanitary conditions can therefore become a problem because manufacturers often instruct end users not to clean the interior of the air ducts for fear of damage to the ducts, and hence a practical and effective way to apply biocide treatment to the inside of the duct is desired to reduce the likelihood of the accumulation and flourishment of microorganisms in the ducts during use.
Therefore, there is a need in the insulation and construction industries for an improved thermally insulated air duct with an improved interior surface. The interior surface should be smooth to reduce friction loss and to resist the accumulation of dirt and other debris. Further, the interior surface must be treatable with biocides to reduce the likelihood of accumulation of microorganisms inside the duct.
A rigid air duct is provided for conducting flowing air, the air duct including a fiber glass board having an interior surface and an exterior surface. The fiber glass board is deformed to cause the interior surface to define a channel for conducting flowing air. The air duct also includes a mat facing adhered to the interior surface of the fiber glass board to provide a smooth air-contacting surface lining the channel to maximize laminar flow of air flowing through the channel. The mat facing is a fabric including glass fibers. The fiber glass board includes fiber glass material and uncured portions of a binder material in the fiber glass material. The mat facing is adhered to the interior surface of the fiber glass board by subjecting the fiber glass board and the mat facing to a temperature which causes curing of the uncured portions of the binder material in the fiber glass material while the mat facing abuts the interior surface of the fiber glass board.
Also in preferred embodiments, an adhesive used to adhere the mat facing to the fiber glass board includes a first portion situated in the fiber glass board and a second portion positioned to lie between the fiber glass board and the mat facing. The first portion is binder material in the fiber glass board.
In preferred embodiments, the fiber glass board further includes a first shiplap edge adjacent to the interior surface and the mat facing is adhered to the shiplap edge. The fiber glass board further includes a second shiplap edge lying in spaced-apart relation to the first shiplap edge to position the interior surface therebetween. The mat facing is adhered to the first and second shiplap edges.
Additional features and advantages of the invention will become apparent to those skilled in the art from the following description of the invention.